During the manufacture of a semiconductor device from a semiconductor substrate, the surface of the substrate can become contaminated with residues. The contamination may be deliberate, for example with the deposition of resist on a surface, or the contamination may be unintentional, for example residues left on a substrate after Chemical Mechanical Polishing (CMP).
One method of removing residues from a surface is to rinse the surface with a mixture of concentrated acid or base and a peroxide. Typically, as described in U.S. Pat. No. 3,900,337, the acid is sulphuric acid. If a base is used, it is typically ammonium hydroxide. The peroxide is typically hydrogen peroxide.
For a hydrogen peroxide/sulphuric acid mixture (which is known as ‘piranha’ solution), peroxy-monosulphuric acid is formed under equilibrium conditions:H2O2+H2SO4HO(SO2)OOH+H2O  (1)
Peroxy-monosulphuric acid is more commonly known as ‘Caro's acid’. It is a strong oxidizing agent and it is thought that this component is particularly effective in removing residues from a substrate.
In the past, two principle methods of removing residues with this type of solution have been used. The first, as described in U.S. Pat. No. 3,900,337, is simply immersing the substrate in a bath containing a mixture of peroxide and acid or base. One problem with this method is that the bath containing the cleaning solution can itself quickly become contaminated with residues, which can lead to reduced cleaning effectiveness. This can also lead to increased financial and environmental costs because the components of the solution need to be changed relatively frequently, and both peroxides and concentrated acids and bases are relatively expensive and have a relatively high environmental impact. In addition, sometimes this method does not adequately remove particularly hard-to-remove residues or contaminants.
The second method is to spray the substrate with a mixture of peroxide and acid or base while rotating or spinning the substrate. The mixture then spreads over the surface of the substrate by virtue of the centrifugal force created by the rotating substrate. An example of this second approach is described in U.S. Pat. No. 5,634,980. One problem with this second approach is that it takes a long time to remove organic residues using this technique. This is especially the case for hard-to-remove residues such as resist. At the same time, the environmental cost of the process increases.
Therefore, the present inventors have researched a new method of removing residues from the surface of a substrate during semiconductor processing. This method is aimed at addressing at least some of the drawbacks of the prior art.